Perez lasted just four innings in the loss, allowing four runs on six hits while walking two and striking out three.
Oakland jumped out to a quick 2-0 lead in the first inning. Josh Reddick drove in Coco Crisp with an RBI single, scoring the game's first run. Chris Carter scored on a balk by Perez later in the inning.
Oakland added two more runs in the fifth, on a Coco Crisp double and Brandon Moss sacrifice fly, giving the A's a 4-2 lead.
Mike Napoli cut into the lead in the seventh, when he belted a solo homer, his third in the last two games, but it wasn't enough as the Rangers fell to the A's.
Jarrod Parker improved to 13-8, pitching six strong innings, allowing three runs on six hits and two walks. Parker struck out six.
The Rangers now just find themselves one game up on the A's with two games left to play. Matt Harrison will start on Tuesday for the Rangers, as Texas looks to avoid a winner-take-all Game 162 in Oakland on Wednesday.